Method and Equipment for Producing Oxidation-Sensitive Liquids Implementing the Injection of Hydrogen Immediately Prior to Pasteurization

ABSTRACT

The invention relates to a method for producing a liquid or semi-liquid product that is sensitive to oxidation, for example beverages, wherein the production method includes a step of deoxygenating an intermediate medium involved in the production of either the liquid or the semi-liquid, and a heating step, for example pasteurization, after the deoxygenation step, characterized in that the method involves injecting a hydrogenated gaseous mixture into the liquid or semi-liquid between the deoxygenation step and the heating step.

The present invention relates to the field of processes for producingoxidation-sensitive liquid or semi-liquid products, and for which themanufacturing process has a heating step, for example a pasteurization,this is the case, for example, for certain food products such as stillor carbonated beverages, fruit juices, flavored waters, compotes orjams, or else dairy products, especially certain cheeses, etc.

Let us consider in what follows the example of beverages, specificallythese beverages see their quality deteriorate, on the one hand duringthe manufacturing process (especially during a pasteurization step), andon the other hand during their subsequent preservation. This phenomenoncan impair both the sensory quality (taste, smell, color, etc.) and thenutritional quality (the vitamin content in particular) of theseproducts. The shelf life of the products is of course adversely affectedthereby.

By way of illustration, it is known from numerous studies that beveragesflavored with citrus fruits, and especially with lemon, are verysensitive to oxidation. Other studies have focused on the effect ofpasteurization on an orange juice and have especially shown that theloss of limonene, which often represents more than 93% of all of thearoma compounds of the concentrate used, amounts to almost 16%. It ispartly due to the oxidation of this molecule which leads to the increaseof limonene oxides: α-terpineol, nerol and geraniol in particular.

Moreover, among the colorants used in this sector, β-carotene(yellow-orange, E 160a) and paprika extracts (orange-red, E 160c) arealso sensitive to oxidation. Likewise, beetroot red (pink-red, E 162)has a limited stability in the presence of oxygen, hence thedifficulties encountered by manufacturers in preserving their beveragescontaining red fruits, the color of which gradually turns brown duringthe storage thereof at ambient temperature. This problem is even morepronounced when the manufacturer wishes, in order to meet theexpectations of the consumer, not to use preservatives. It is importantto note that the color is the first product characteristic that theconsumer sees on the shelf, that is to say an important, sometimes evendecisive, purchase factor.

In the event of the presence of oxygen, the oxidation may be rapid inthe treatment steps where the product is heated, in particular in anoptional pasteurization step. The oxidation is obviously slower when theproduct is at ambient temperature, in particular during its storageperiod. Some factors may however contribute to a fasterdegradation/oxidation during this period, in particular the exposure ofthe product to light, the diffusion of oxygen through the packaging,etc.

Oxidation is frequently attributed to the oxygen permeability of plasticpackagings. Indeed, irrespective of the quality of the inerting duringbottling (residual amount of oxygen in the headspace of the packaging),the residual dissolved oxygen contained in the product during thepackaging thereof and the diffusion over time of oxygen through thepackaging mean that it is difficult, or even impossible, for certaincontainers to completely eliminate the risk of oxidation over time.However, it is possible to at least partially delay the oxidation.Indeed, a predominant portion of the oxidation is based on radicalreactions, radicals produced inter alia by dissolved oxygen, light andorganic initiator and propagator compounds.

Limiting the latter compounds makes it possible to limit the oxidation,in particular during the product storage period. It is thereforeessential that the oxidation process cannot begin at the step ofproducing the beverage or one of its ingredients.

The literature has revealed that the oxidation mechanisms take placeaccording to three distinct phases:

1—Initiation:

The initial reaction mechanism consists of the formation of a freeradical by pulling off a hydrogen atom.

RH→R.+H.

The oxidation is firstly very slow due to the low initiation rate.Indeed, the departure of the hydrogen atom is not very likely due to thehigh activation energy of the reaction. It is however facilitated byheating, light or metal ions.

2—Propagation:

In the presence of oxygen, the R. free radical reacts in order to resultin the formation of a peroxyl radical ROO.. The latter stabilizes itsstructure by pulling off a hydrogen atom from another molecule R′H. Thefree radical R′. thus formed is highly reactive and may continue thereaction according to the same principle (loop reactions).

R.+O₂→ROO.

ROO.+R′H→ROOH+R′.

3—Termination:

When the concentration of free radicals becomes high enough, the lattercombine in order to stop the propagation chain.

R.+R′OO.→ROOR′

R.+R′.→RR′

2ROO.→ROOR+O₂

Molecules known as “antioxidants” (AH₂), that is to say that have aredox potential lower than that of the free radicals, may also stop theoxidation. Thus, for example, amines, phenols, sulfide derivatives andcertain polycondensed aromatic hydrocarbons are weak inhibitors ofoxidation reactions.

R.+AH₂→RH+AH.

ROO+AH₂→ROOH+AH.

It is then understood that this industrial sector is constantly seekingprocesses that make it possible to limit the oxidation of theseproducts, in order to extend their best-before date and thus reduce thecosts for the manufacturer.

In addition, it is also understood that one of the means identified forfighting the oxidation of sensitive liquids is to delay or limit theinitiation phase. For this, it is necessary to act before the heatingstep, in order to reduce the production of R. and ROO. free radicals,which are the precursors or initiators of the oxidative chain reactionswhich will deteriorate the product during the propagation phase.

This industry has proposed various technical solutions, among whichmention may be made of the following approaches:

I) The Use of Antioxidants

The main antioxidants used in food products are:

-   -   ascorbic acid and its sodium and calcium salts and also its        ascorbyl palmitate and ascorbyl stearate esters (E 300 to E        304ii),    -   tocopherols (E 306 to E 309),    -   esters of gallic acid: propyl, octyl and dodedyl gallate (E 310        to E 312),    -   butylhydroxyanisole (BHA, E 320),    -   butylhydroxytoluene (BHT, E 321).

The use of antioxidants is however subject to regulatory constraints(restriction of use, dose to be complied with). Thus, for example, infruit juices and nectars, only the following antioxidants areauthorized: E 300 and E 301 according to the Parliament and CouncilDirective 95/2/EC. BHA and BHT are themselves used, for example, asantioxidants in the solutions of flavorings that are incorporated intothe composition of beverages.

The use of additives has several drawbacks, among which the legalobligation to include the list thereof on the labeling of the finishedproduct. Furthermore, additives in general, and therefore antioxidants,are very often, due to their nomenclature (E XXX), likened to“chemicals” that are “not natural” by consumers. Furthermore, not onlydo they convey a negative image, but they are not always sensoriallyneutral.

Certain additives may give rise to physiological disorders (BHA and BHTin particular), and it is then advisable to adapt their dosage in orderto comply with the acceptable daily intake defined in the legislation.This constraint can limit their effectiveness.

Furthermore, ascorbic acid, erythorbic acid and ascorbyl palmitate arenot very heat-stable whilst gallates are heat-sensitive.

Finally, the mechanisms of action of antioxidants have an effectivenesswhich remains however limited since they are very easily oxidizablemolecules (low reducing power).

J) Deoxygenation: Under Vacuum or Under Gas (Degassing)

Deoxygenation is one way of fighting the oxidation phenomena and thusincreasing the storage life of a product. This step of deoxygenation (ordegassing) may be carried out either by a process based on placing theproduct under complete or partial vacuum, or by a gaseous entrainment ofthe dissolved oxygen by injection of an inert gas, process commonlyknown as “stripping”.

By way of example, mention may be made of patent U.S. Pat. No.2,151,644, which proposes a method for deaerating a liquid food productby continuously circulating a liquid in film form in a vacuum chamber.Similarly, document WO 2005/004643 proposed a continuous deaeration oflemon juice at low temperature (˜0° C. to 10° C.) and under vacuum.

Document WO 2006/039674 itself claims the use of porous-type injectorsin order to introduce nitrogen in the form of small bubbles at variouspoints of the production line in order to reduce the amount of oxygendissolved in lemon juice.

The deoxygenation technologies, whether they use vacuum or an inert gassuch as nitrogen, make do with partly expelling the oxygen present inthe liquid. Thus, they make it possible, for example, to limit theaerobic degradation pathway of vitamin C and the appearance of browningin an orange juice. However there still remains residual oxygen, or evenoptionally oxidizing agents comprising oxygen combined, in particular ofnitrate and sulfate type, capable of reacting in order to oxidize thesensitive molecules. In that regard, this solution is not thereforecompletely satisfactory.

K) Deoxygenation with a Gas Mixture Containing Hydrogen

The applicant proposed in document FR 2 811 292 a process for packagingperishable products comprising, in particular, the possibility ofintroducing into a liquid product a protective gas comprising a certainamount of hydrogen, the balance being formed by one or more packaginggases. It will have been understood that this prior process is thereforeonly interested in the packaging stage, that is to say after thepasteurization step. It therefore makes it possible to protect theliquid during the storage thereof, but it does not make it possible toprotect it from the oxidation that is initiated during thepasteurization.

Other studies have investigated, on the laboratory scale (150 mL), theimpact of nitrogen or nitrogen-hydrogen (96% N₂, 4% H₂) bubbling beforepasteurization on the microbiological quality, the color and the contentof ascorbic acid of an orange juice, and showed that a deoxygenation,with nitrogen or nitrogen-hydrogen, leads to a loss of effectiveness ofthe pasteurization (less microorganisms killed) compared to the sameprocess without prior deoxygenation. Furthermore, after seven weeks ofstorage, the authors observe that the fact of deoxygenating beforepasteurization has improved the stability of ascorbic acid and that ofthe color compared to the absence of prior deoxygenation. However, theydo not observe a significant difference between a deoxygenation usingnitrogen and a deoxygenation using nitrogen-hydrogen. At the end of thisstudy, the authors therefore recommend introducing the gas into theliquid just after pasteurization so as to maximize the destruction ofthe microorganisms while stabilizing the product during its storage.

As will be seen in greater detail in what follows, the present inventionproposes a novel process for manufacturing a liquid or semi-liquidproduct such as those targeted above, undergoing a heating step, inparticular a pasteurization step, that makes it possible to limit theformation of compounds that may act as radical initiators and/orpropagators in the oxidation reactions during the storage period of theproducts, and thus that makes it possible to increase their storagelife.

The novel approach of the invention is based on the fact that it doesnot make do, as proposed by the prior art, with deoxygenating theproduct before pasteurization, it proposes to combine a step ofdeoxygenation, irrespective of the process used (vacuum, purging with aninert gas, with a gas mixture containing hydrogen, etc.), with theinjection of a hydrogen-containing gas mixture between the deoxygenationstep and the heating step, preferably just before the heating step, andas will be seen this amount may be minimal. This injection makes itpossible to use the reducing nature of the hydrogen in an optimalmanner, due to being under very favorable conditions, since the hydrogeninjected will be able to act immediately afterward (during the heating)at a temperature above ambient temperature.

The present invention then relates to a process for producing anoxidation-sensitive liquid or semi-liquid product, which productionprocess comprises a step of deoxygenation of an intermediate medium thatoccurs in the manufacture or else of the liquid or semi-liquid itself,and which comprises a heating step, for example a pasteurization,subsequent to the deoxygenation step, being characterized in that,between the deoxygenation step and the heating step, ahydrogen-containing gas mix is injected into the liquid or semi-liquid.

It will have been understood that, in most cases, the deoxygenationtakes place in the liquid or semi-liquid medium itself (the pure juice,or else the already flavored water, the compote, etc.) but it may alsohappen that the deoxygenation step takes place in an intermediate mediumthat occurs in the manufacture. By way of example, in the case of afruit juice based on concentrate, it can be envisaged to deoxygenate thewater alone first, then add the concentrate, before carrying out theinjection of gas according to the invention.

According to advantageous embodiments of the invention, the inventionwill be able to adopt one or more of the following technical features:

-   -   the hydrogen-containing gas mix is pure hydrogen;    -   the hydrogen-containing gas mix is a mixture of nitrogen and        hydrogen, the hydrogen content of which is between 1% and 100%,        but preferably lying between 50% and 100%;    -   the deoxygenation step of the intermediate or liquid or        semi-liquid medium is carried out by placing the intermediate        medium or the liquid or semi-liquid in question under complete        or partial vacuum;    -   the deoxygenation step is carried out by injection of an inert        gas or of a gas mixture comprising a reducing gas such as        hydrogen into the liquid medium or the liquid or semi-liquid in        question;    -   the injection of the hydrogen-containing gas mixture between the        deoxygenation step and the heating step is carried out just        before the heating step, typically by taking into account the        time needed for the transfer of the hydrogen into the liquid        phase, and therefore preferably from 5 s to 30 s before the        heating step.

The present invention also relates to a plant for producing anoxidation-sensitive liquid or semi-liquid product, which plant comprisesa device for the deoxygenation of an intermediate medium that occurs inthe manufacture or else of the liquid or semi-liquid itself, and also adevice for heating this liquid or semi-liquid, located downstream of thedeoxygenation device, being characterized in that it comprises a devicefor injecting a hydrogen-containing gas mix into the liquid orsemi-liquid, located between the deoxygenation device and the heatingdevice.

According to one of the embodiments of the invention, the device forinjecting the hydrogen-containing gas may be the same as thedeoxygenation device when the deoxygenation is carried out by injectingan inert or non-inert gas such as a hydrogen-containing gas (loopoperation).

Other features and advantages of the present invention will appear moreclearly in the following description, given by way of illustration butin no way limitingly, and made in connection with the appended figureswhere:

FIG. 1 is a simplified diagram that makes it possible to visualize thelocations where the invention takes place;

FIG. 2 is a partial schematic representation of a plant formanufacturing and bottling beverages in accordance with the invention,having enabled the implementation of exemplary embodiments;

FIG. 3 is a variant of the plant from FIG. 2, which does not use coolingafter pasteurization, and that combines the injections A and B from FIG.2 in a single injection.

The following steps are recognized in FIG. 1:

-   -   step a) of “liquid preparation”, which is a step of        reconstituting the liquid, for example the production of the        mixture of water, juice concentrate and pulp, or else the        production of a mixture of water+various flavoring ingredients        in the case of a flavored water, but it is understood that this        preparation step may be nonexistent in certain cases or else        reduced to the minimum by the fact that the liquid is already        completely ready (for example what is referred to as a “pure        juice”);    -   step b) which is a deoxygenation step, for example via injection        of an inert gas into the liquid. It should be noted that in        order to carry out the deoxygenation, the injection alone of        nitrogen or of another gas is not sufficient, as is known, the        liquid will have to pass, later on in the production line, into        equipment that enables the oxygen-laden gas to come out of the        liquid and the line.

As has been said, this deoxygenation may be carried out by vacuum but agas purging will be preferred, on the one hand to prevent the subsequent“collapsing” of the packaging, and on the other hand to reduce the lossof aroma compounds at this step. Without forgetting the fact that thegaseous method is less energy-consuming and requires a lower equipmentinvestment.

An addition of ingredients may optionally take place after thisdeoxygenation. Thus, for example in the case of a concentrate-basedfruit juice, it can be envisaged to deoxygenate the water then add theconcentrate after step b) and before step c). In this case, it ispossible to carry out the sequence b) then c) (then b) again ifnecessary) then d), etc.

This introduction of an inert gas into the liquid makes it possible toshift the oxygen from the liquid phase to the gas phase. Thisdeoxygenation may take place in the tank, the headspace of which isinerted, or else in line in equipment well known to a person skilled inthe art.

-   -   step c) which consists in injecting a hydrogen-containing        mixture, here pure hydrogen, into the liquid;    -   step d) of pasteurization;    -   very often, there is a step e) of cooling the product downstream        of the heating step and before the packaging of the product, but        this cooling is only optional;    -   the liquid resulting from the pasteurization (or from the        cooling) then being sent toward the downstream of the line (f)),        that is to say toward the next steps of the production of this        liquid, for example a bottling of the beverage.

As is understood, it is highly preferable, downstream of thedeoxygenation step b) to ensure that all the tanks and other equipmentinto which the liquid passes are carefully inerted, including theequipment used downstream of the pasteurization, and especially thefinal packaging f).

As indicated above, the amount of hydrogen added just beforepasteurization may be minute.

When the curve (much referenced in the literature) which represents thesolubility of hydrogen in water at atmospheric pressure as a function oftemperature is considered, it is observed for example that thissolubility is of the order of 1.6 mg/l at 20° C. under around 1 bar.Still referring to the curves from the literature at differentpressures, it is of the order of 4.8 mg/l at 20° C. under around 3 bar.

FIG. 2 is a partial schematic representation of a plant formanufacturing and bottling beverages that enables the implementation ofthe invention.

This beverage production line enables the bottling of an hourlythroughput of 10 m³/h of liquid.

Found in this FIG. 2 are of course the essential elements of theschematic representation of FIG. 1, and in particular:

-   -   the tank for preparing the beverage or for storing a pure fruit        juice for example, this tank undergoing here two injections of        nitrogen: injection A into the liquid, intended to move oxygen        from the liquid phase to the gas phase, and injection B, into        the top of the tank, which serves to inert the tank (these two        injections may where appropriate be combined, see FIG. 3);    -   the injection in line (C) into the liquid, just upstream of the        pasteurization device, of a flow rate of 0.18 Nm²/h of pure        hydrogen, this injection will be carried out, for example, by        means of a porous-type injector, of a static mixer, or else        Venturi, or any other equivalent equipment.

The injector is therefore positioned on the line upstream of thepasteurization heat exchanger, preferably by leaving a contact timeafter injection of between 5 and 30 s.

The amount of hydrogen injected will preferably be between thesaturation value at ambient temperature under one atmosphere and thesaturation value under the same temperature conditions at the pressureof the beverage line.

For the exemplary embodiment from FIG. 2, which is a production lineunder 3 bar, the amount injected is preferably between 16 and 48 g/h ofhydrogen, i.e. between 0.18 and 0.54 Nm³/h of pure hydrogen.

-   -   downstream of the pasteurization equipment and after cooling of        the product an inerted buffer tank (injection D) is positioned,        this tank may be inerted in static mode (without renewal of the        overhead), or in purging mode (renewed, which is preferred). In        the latter case and in order to eliminate any risk of excessive        concentration of hydrogen in the atmosphere, it is preferable to        purge the headspace of the buffer tank with an inert gas, for        example nitrogen at a minimum flow rate so that the hydrogen        concentration in the gas phase is under any circumstances less        than 4%, thus, as is known, eliminating any related risk.

For the exemplary embodiment for this FIG. 2, put in place at D is apurging flow rate of the overhead by an inert gas at a minimum flow rateof QN₂=0.18/0.04=4.5 Nm³/h, i.e. around 0.5 Nm³ of nitrogen per cubicmeter of beverage produced.

The measurements carried out on the fruit juices thus produced, afterall of the steps and after three days of storage show a residualhydrogen level equal to 25% of the saturation in glass bottles at 20°C., and equal to 4% in PET bottles.

Every advantage that there is in carrying out an injection of hydrogenor of a hydrogen-containing mixture at the location where it isenvisaged according to the invention is then understood since in thisway:

-   -   it takes place at a location where the liquid is already        deoxygenated;    -   it does not take place too early in the process, at the risk        that the hydrogen is eliminated at the time of the degassing and        with the unfavorable consequence that the hydrogen will no        longer be present at the time of the heating;    -   it does not take place too late in the process, for example        after the pasteurization, since, and this is the very inventive        measure of the present invention, it is desired for the        dissolved hydrogen to be present during this pasteurization step        in order to prevent the formation of oxidation precursors during        the heating.

Other advantages of the process of the invention compared to the priorsolutions may be summarized in what follows:

-   -   It is easily adapted to the existing line.    -   It does not represent a sizable investment.    -   It does not make do with expelling oxygen.    -   It does not have sensory or legal constraints, nor an impact on        human physiology.    -   It benefits from the highly reducing power of hydrogen (compared        to the antioxidants used customarily), without having to add        mineral and/or organic additives.    -   It does not increase the labeling (list of ingredients).    -   It does not lead to additional flavor losses.

1-7. (canceled)
 8. A process for producing an oxidation-sensitive liquidor semi-liquid product, which production process comprises a step ofdeoxygenation of an intermediate medium that occurs in the manufacturingof the liquid or semi-liquid itself, and which comprises a heating step,for example a pasteurization, subsequent to the deoxygenation step,wherein, between the deoxygenation step and the heating step, ahydrogen-containing gas mix is injected into the liquid or semi-liquid.9. The process for producing an oxidation-sensitive liquid orsemi-liquid product of claim 8, wherein the hydrogen-containing gas mixis pure hydrogen.
 10. The process for producing an oxidation-sensitiveliquid or semi-liquid product of claim 8, wherein thehydrogen-containing gas mix is a mixture of nitrogen and hydrogen, thehydrogen content of which is between 1% and 100%, preferably between 50%and 100%.
 11. The process for producing an oxidation-sensitive liquid orsemi-liquid product of claim 8, wherein the deoxygenation step iscarried out by placing under complete or partial vacuum.
 12. The processfor producing an oxidation-sensitive liquid or semi-liquid product ofclaim 8, wherein the deoxygenation step is carried out by injection ofan inert gas or of a gas mixture comprising a reducing gas such ashydrogen.
 13. The process for producing an oxidation-sensitive liquid orsemi-liquid product of claim 8, wherein the injection of thehydrogen-containing gas mixture between the deoxygenation step and theheating step is carried out just before the heating step, preferablyfrom 5 s to 30 s before the heating step.
 14. A plant for producing anoxidation-sensitive liquid or semi-liquid product, which plant comprisesa device for the deoxygenation of an intermediate medium that occurs inthe manufacture or else of the liquid or semi-liquid itself, and also adevice for heating the liquid or semi-liquid, located downstream of thedeoxygenation device, being characterized in that it comprises a devicefor injecting a hydrogen-containing gas mix into the liquid orsemi-liquid, located between the deoxygenation device and the heatingdevice.